A mobile communications network is typically made up of a plurality of cells. Each cell includes a radio base station, with each base station connected to a mobile switching center or a packet service node that manages communications sessions between mobile stations and terminals coupled to a public switched telephone network (PSTN) or a packet-based data network. Communications between mobile stations and base stations are performed over wireless links.
Traditional wireless protocols provide for circuit-switched communications. Such protocols include time-division multiple access (TDMA) protocols and code-division multiple access (CDMA) protocols. In a circuit-switched network, a channel portion between two endpoints (e.g., two mobile stations) is occupied for the duration of the connection between the endpoints.
With the wide availability of the Internet and intranets, packet-switched communications (e.g., web browsing, electronic mail, and so forth) have become more common. Generally, a circuit-switched connection is an inefficient mechanism for communicating packet data. As a result, third generation (3G) and beyond wireless technologies are being developed and implemented to provide higher bandwidth and more efficient packet-switched communications (of data as well as voice and other forms of real-time data) over wireless networks.
One example of a packet-switched wireless technology is defined by the CDMA2000 family of standards, developed by the Third Generation Partnership Project 2 (3GPP2). A CDMA2000 wireless communications network is capable of supporting both circuit-switched services and packet-switched services. For TDMA, packet-switched wireless communications protocols have also been developed, such as the Enhanced General Packet Radio Service (EGPRS) protocol as defined by the 3GPP (Third Generation Partnership Project) UMTS (Universal Mobile Telecommunications System) Release 1999 Standard, and others.
A popular technique of communicating voice in packet-switched communications is referred to as voice-over-Internet Protocol (IP). In voice-over-IP, voice (and other forms of real-time data) is carried in IP packets in an IP session established between two or more network devices. With advancements in packet-switched wireless technologies, voice-over-IP over packet-switched wireless networks have also been implemented.
A more recent advancement is the proposal of press (push)-to-talk (PTT) over voice-over-IP in a wireless network. This technology is based on PTT over cellular (PoC) technology, which enables real-time one-to-one or one-to-many voice communications service over a wireless network that is started by pressing or pushing a talk key or button on a mobile station. PTT enables multiple users to communicate with each other, where one party (the caller) has control and right-to-speak at any one time. To acquire the right-to-speak, the caller sends a request (referred to as a floor control request) to a PTT server, where the request is sent in response to pushing of the talk key or button on a mobile station.
Data service applications, such as PTT applications or other types of data service applications, are associated with both control and data traffic. Traditionally, two traffic flows over the wireless link between a mobile station and a base station system are established for separately carrying the application control information and application data information (e.g., voice). Different service options are used for the two traffic flows. For example, in a CDMA2000 wireless network, the traffic flow for carrying application control information uses a service option (e.g., service option 33 or SO-33) with the Radio Link Protocol (RLP) enabled. RLP provides a reliability mechanism to assure retransmission of lost application control information in the traffic flow over the wireless link, which can be lost due to poor wireless conditions. On the other hand, the traffic flow for carrying application data, such as voice, is associated with another service option (e.g., SO-60) in which RLP (and its associated reliability mechanism) is disabled.
Typically, it is not desirable to retransmit lost voice data, since vocoders (voice encoders/decoders) are able to conceal error (by replaying previously received good voice frames). Any reliability mechanism defined for retransmitting voice traffic would increase the delay for transmitting voice over the wireless link. However, an issue associated with using multiple traffic flows over the wireless link for separately carrying application control information and application data information is inefficiency in allocation of resources of the wireless link.
In some other wireless systems, a single traffic flow, with RLP enabled, has been used to carry both application control and data information. However, the provision of RLP for carrying real-time application data information is inefficient due to the increased delay and the increased delay variation, which have negative effects on the quality of service.